Enhancement of second harmonic generation and photocurrent generation of anovel stilbazolium dye dimer in Langmuir-Blodgett monolayer films

A novel amphiphilic stilbazolium dye dimer, bis{[1-(N-methyl-4-pyridinium)- 2-(4-N-methyl- N-hexadecylaminophenyl)]ethenyl}methanediiodide (C1BP) was s ynthesized, and (E)-N-methyl-4-[2-(4-N-methyl-N-hexadecylaminophenyl)etheny l]pyridinium iodide (C1P) as a standard for comparison was also synthesized . They were successfully transferred onto the semiconducting transparent in dium-tin oxide (ITO) or quartz as H-aggregates by the Langmuir-Blodgett (LB ) technique. This centrosymmetric dimer (C1BP) can exhibit strong second-ha rmonic generation (SHG) by the LB method. The second harmonic susceptibilit y chi ((2)) of the monolayer film reaches 167 pm V-1 for C1BP and that for C1P is 125 pm V-1. The photoelectrochemistry of these dyes monolayer films was investigated in a traditional three-electrode cell. Steady cathodic pho tocurrent is obtained upon excitation of the dyes in LB films deposited on an ITO electrode. The observed photocurrent generation quantum yield strong ly depended on the applied electrode potential, concentration of the redox couples in the electrolyte solution, and chemical structure of the dye cong eners. The results show that the photocurrent generation property of the di mer is enhanced. The photocurrent generation quantum yield is 0.51% for C1B P, while that for C1P is 0.30%.